1. Field of the Invention
The present invention relates to an aluminum alloy and a method for manufacturing an aluminum-alloy member and, more particularly, to an aluminum alloy combining good forgeability and high hardness and a method for manufacturing an aluminum-alloy member combining good forgeability and high hardness.
2. Description of the Background Art
High-strength aluminum alloys have been in use in recent years that are produced by adopting a rapid solidification technique.
For instance, a published Japanese patent application Tokukaihei 1-275732 has disclosed that rapid solidification of a multi-element alloy expressed by a general formula AaMbXc produces a nanocrystalline aluminum alloy having such mechanical properties as a tensile strength of 853 to 1,009 MPa, a yield strength of 804 to 941 MPa, and a hardness HV of 200 to 1,000. In the above formula AlaMbXc, (1) xe2x80x9cMxe2x80x9d means one or more kinds of metal elements selected from the group consisting of chrome(Cr), manganese(Mn), iron(Fe), cobalt(Co), nickel(Ni), copper(Cu), zirconium(Zr), titanium(Ti), magnesium(Mg), and silicon(Si), (2) xe2x80x9cXxe2x80x9d means one or more kinds of metal elements selected from the group consisting of yttrium(Y), lanthanum(La), cerium(Ce), samarium(Sm), neodymium(Nd), niobium(Nb), and mischmetal(Mm), and (3) xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d, and xe2x80x9ccxe2x80x9d mean an atomic percent, xe2x80x9caxe2x80x9d lying in the range of 50 to 95 atm. %, xe2x80x9cbxe2x80x9d in the range of 0.5 to 35 atm. %, and xe2x80x9ccxe2x80x9d 0.5 to 25 atm. %.
Another published Japanese patent application Tokukaihei 6-184712 has disclosed an aluminum alloy having the composition expressed by a general formula AlaLnbMc, where (1) xe2x80x9cLnxe2x80x9d means one or more kinds of metal elements selected from the group consisting of mischmetal, yttrium, lanthanum, cerium, samarium, neodymium, hafnium, niobium, and tantalum, (2) xe2x80x9cMxe2x80x9d means one or more kinds of metal elements selected from the group consisting of vanadium, chrome, manganese, iron, cobalt, nickel, copper, zirconium, titanium, molybdenum, tungsten, calcium, lithium, magnesium, and silicon, and (3) xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d, and xe2x80x9ccxe2x80x9d mean an atomic percent, xe2x80x9caxe2x80x9d lying in the range of 50 to 97.5 atm. %, xe2x80x9cbxe2x80x9d in the range of 0.5 to 30 atm. %, and xe2x80x9ccxe2x80x9d 0.5 to 30 atm. %. The aluminum alloy is a rapidly solidified aluminum alloy that has a cellular composite structure in which 5 to 50 vol. % amorphous phases surround nanocrystalline phases. The aluminum alloy is subjected to plastic working at a temperature higher than the crystallization temperature of the amorphous phase. Intermetallic compounds comprising two or more kinds of the above-described Al, xe2x80x9cLnxe2x80x9d, and xe2x80x9cMxe2x80x9d are dispersed in the nanocrystalline matrix to form a structure having such mechanical properties as a tensile strength of 760 to 890 MPa and an elongation of 5.5 to 9.0%.
However, the aluminum alloy disclosed in the application Tokukaihei 1-275732 has poor ductility and toughness, though it has very high tensile strength and hardness. Because this lack of sufficient ductility and toughness allows easy generation of cracks at the time of processing such as forging and upsetting, it is difficult to perform near-net-shape forging with complicated shapes.
When forging is carried out by exploiting its superplasticity resulting from its nanocrystallinity, it is possible to impart complicated shapes. However, its poor ductility and toughness requires prolonged time for a single step of forging, causing a problem of reduced production efficiency, and hence an increase in manufacturing costs. Such a problem becomes serious when forming ornamental components that require complicated, fine shapes such as embossed letters on the surface.
Although the aluminum alloy disclosed in the application Tokukaihei 6-184712 ensures a certain amount of ductility, it does not have sufficient mechanical properties to undergo near-net-shape forging with complicated shapes. In addition to that, because it uses material powders in which amorphous layers are formed, there is a problem of increased material cost.
The present invention is aimed at solving the above-described problems. An object of the present invention is to offer an aluminum alloy that not only has high hardness accompanied by balanced ductility but also has high toughness and superior processability.
Another object of the present invention is to offer a method for manufacturing an aluminum-alloy member that not only has high hardness accompanied by balanced ductility but also has high toughness and superior processability.
The first aspect of the present invention offers an aluminum alloy that comprises (1) not less than 0.1 wt. % and not more than 8 wt. % Constituent A comprising one or more kinds of elements selected from the group consisting of titanium (Ti), vanadium (V), hafnium (Hf), and zirconium (Zr), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li).
The second aspect of the present invention offers another aluminum alloy that comprises (1) not less than 0.1 wt. % and not more than 5 wt. % Constituent D comprising one or more kinds of elements selected from the group consisting of niobium (Nb), molybdenum (Mo), silver (Ag), iron (Fe), cobalt (Co), tantalum (Ta), and tungsten (W), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li).
The third aspect of the present invention offers a method for manufacturing an aluminum-alloy member made of the following aluminum alloy: The aluminum alloy comprises (1) not less than 0.1 wt. % and not more than 8 wt. % Constituent A comprising one or more kinds of elements selected from the group consisting of titanium (Ti), vanadium (V), hafnium (Hf), and zirconium (Zr), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li). First, a preform comprising the aluminum alloy is produced. Next, the preform is heated up to a temperature not lower than 200xc2x0 C. and not higher than 600xc2x0 C. at a temperature rising rate of not less than 2xc2x0 C./sec and not more than 200xc2x0 C./sec. Then, the heated preform is subjected to hot-working.
The fourth aspect of the present invention offers a method for manufacturing an aluminum-alloy member made of the following aluminum alloy: The aluminum alloy comprises (1) not less than 0.1 wt. % and not more than 5 wt. % Constituent D comprising one or more kinds of elements selected from the group consisting of niobium (Nb), molybdenum (Mo), silver (Ag), iron (Fe), cobalt (Co), tantalum (Ta), and tungsten (W), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li). First, a preform comprising the aluminum alloy is produced. Next, the preform is heated up to a temperature not lower than 200xc2x0 C. and not higher than 600xc2x0 C. at a temperature rising rate of not less than 2xc2x0 C./sec and not more than 200xc2x0 C./sec. Then, the heated preform is subjected to hot-working.
The first to fourth aspects of the present invention offer an aluminum alloy that not only has high hardness accompanied by balanced ductility but also has high toughness and superior processability and a method for manufacturing an aluminum-alloy member that not only has high hardness accompanied by balanced ductility but also has high toughness and superior processability.
The first aspect of the present invention offers an aluminum alloy that comprises (1) not less than 0.1 wt. % and not more than 8 wt. % Constituent A comprising one or more kinds of elements selected from the group consisting of titanium (Ti), vanadium (V), hafnium (Hf), and zirconium (Zr), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li).
Such a composition facilitates the formation of complicated shapes because it reduces the strength of the aluminum alloy in the temperature range for processing. This reduces the number of times of forming (forging) until the last shape in comparison with the conventional products, and therefore reduces the processing cost.
This composition also increases the hardness of the aluminum alloy, and increased hardness suppresses the generation of surface flaws on members made of the aluminum alloy of the present invention during their manufacturing processes, reducing the fraction defective of the products.
The addition of a small amount of Ti, V, Hf, and Zr, which are used in Constituent A, can reduce the grain size of aluminum, increasing the hardness of the aluminum alloy. Intermetallic compounds between these elements and aluminum are deposited or crystallized out at the center of the individual crystal grains of aluminum (one place per crystal grain). If the content of Constituent A is less than 0.1 wt. %, the above-mentioned effect of increased hardness cannot be obtained. If the content of Constituent A is more than 8 wt. %, although the hardness of the aluminum alloy increases, the ductility, critical upsetting ratio, and other properties decrease, making it difficult to perform near-net-shape forging with complicated shapes, resulting in the reduction in forgeability.
The above-mentioned upsetting ratio is expressed in (L0xe2x88x92L1)/L0xc3x97100 (%), where L0 is the sample length in the upsetting direction before the upsetting work, and L1 after the upsetting work. The critical upsetting ratio is defined as the upsetting ratio at which cracks begin to develop at the periphery of the workpiece when upsetting is performed at a forging rate of 0.5 mm/sec. If the critical upsetting ratio is 70% or more, the sample is considered to have sufficient forgeability.
The elements La, Ce, Pr, Nd, Mm, Ca, Sr, and Ba, which are used in Constituent B, have an effect that a small amount of their addition can deposit a large amount of intermetallic compounds having high hardness. The deposition of intermetallic compounds increases the hardness of the aluminum alloy. The intermetallic compounds between these elements and aluminum are deposited or crystallized out at grain boundaries of aluminum. If the content of Constituent B is less than 0.1 wt. %, the above-mentioned effect cannot be obtained. If the content of Constituent B is more than 20 wt. %, although the hardness of the aluminum alloy increases, the ductility and other properties deteriorate, reducing the forgeability.
The elements Mg and Li, which are used in Constituent C, have an effect that they can increase the hardness of the aluminum alloy when they are rapidly solidified in xcex1-aluminum to form a supersaturated solid solution. If the content of Constituent C is less than 0.1 wt. %, the above-mentioned effect cannot be obtained. If the content of Constituent C is more than 20 wt. %, although the hardness of the aluminum alloy increases, the ductility, critical upsetting ratio, and other properties deteriorate, reducing the forgeability.
When Constituents A, B, and C are added with the specified contents as shown above, because the aluminum having Constituent C as a solid solution has fine crystal grains and because the intermetallic compounds are deposited or crystallized out at grain boundaries, a structure is formed that has less tendency to overgrow with temperature. The formation of this structure enables the production of an aluminum alloy with superior balance between the hardness and forgeability.
If any one of Constituents A, B, and C lies beyond the specified range of content, the balance between the hardness and forgeability is destroyed, producing high hardness with low forgeability or high forgeability with low hardness.
When an aluminum alloy having the above-described structure is hot-worked and then its surface is polished by buffing or other means, the surface of the member made of this hot-worked aluminum alloy can easily obtain metallic luster.
In the aluminum alloy of the first aspect of the present invention, it is more desirable that the content of Constituent C be more than 5 wt. % and not more than 20 wt. %.
This content range, when the surface of the aluminum alloy is anodized to form an anodic oxide coating, enables the anodic oxide coating to obtain a shade of relatively low brightness such as brown or dark gray.
The shade of the anodic oxide coating can be changed by adjusting the kind and content of elements used in Constituent C and other Constituents.
The aluminum alloy of the first aspect of the present invention may further comprise not less than 0.1 wt. % and not more than 5 wt. % Constituent D comprising one or more kinds of elements selected from the group consisting of niobium (Nb), molybdenum (Mo), silver (Ag), iron (Fe), cobalt (Co), tantalum (Ta), and tungsten (W).
This can offer an aluminum alloy having good forgeablity and higher hardness.
The elements Nb, Mo, Ag, Fe, Co, Ta, and W, which are used in Constituent D, have an effect that they can not only reduce the grain size of aluminum but also deposit a large amount of intermetallic compounds. As a result, the hardness of the aluminum alloy can be further increased. In this case, the intermetallic compounds are deposited or crystallized out at a plurality of places inside the individual crystal grains of the aluminum.
If the content of Constituent D is less than 0.1 wt. %, the above-mentioned effect cannot be obtained. If the content of Constituent D is more than 5 wt. %, although the hardness of the aluminum alloy increases, the ductility, critical upsetting ratio, and other properties deteriorate, reducing the forgeability.
In the aluminum alloy of the first aspect of the present invention, it is more desirable that Constituent A be Zr, Constituent B be Mm, and Constituent C be Mg. In this case, it is more desirable that the content of Constituent A be not less than 0.1 wt. % and not more than 3 wt. % and the content of Constituent B be not less than 0.1 wt. % and not more than 15 wt. %.
The respective use of Zr, Mm, and Mg as Constituents A, B, and C can offer an aluminum alloy with further enhanced balance between the hardness and forgeability.
The second aspect of the present invention offers another aluminum alloy that comprises (1) not less than 0.1 wt. % and not more than 5 wt. % Constituent D comprising one or more kinds of elements selected from the group consisting of niobium (Nb), molybdenum (Mo), silver (Ag), iron (Fe), cobalt (Co), tantalum (Ta), and tungsten (W), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li).
Such a composition facilitates the formation of complicated shapes because it reduces the strength of the aluminum alloy in the temperature range for processing. This reduces the number of times of forming (forging) until the last shape in comparison with the conventional products, and therefore reduces the processing cost.
This composition also increases the hardness of the aluminum alloy. Increased hardness suppresses the generation of surface flaws on members made of the aluminum alloy of the present invention during their manufacturing processes, reducing the fraction defective of the products.
The elements Nb, Mo, Ag, Fe, Co, Ta, and W, which are used in Constituent D, have an effect that they can not only reduce the grain size of aluminum but also deposit a large amount of intermetallic compounds. As a result, the hardness of the aluminum alloy can be further increased. The intermetallic compounds produced by Constituent D are deposited or crystallized out at a plurality of places inside the individual crystal grains of the aluminum. If the content of Constituent D is less than 0.1 wt. %, the above-mentioned effect cannot be obtained. If the content of Constituent D is more than 5 wt. %, although the hardness of the aluminum alloy increases, the ductility, critical upsetting ratio, and other properties deteriorate, reducing the forgeability.
The elements La, Ce, Pr, Nd, Mm, Ca, Sr, and Ba, which are used in Constituent B, have an effect that a small amount of their addition can deposit a large amount of intermetallic compounds having high hardness. The deposition of intermetallic compounds increases the hardness of the aluminum alloy. The intermetallic compounds produced by Constituent B are deposited or crystallized out at grain boundaries of aluminum.
If the content of Constituent B is less than 0.1 wt. %, the above-mentioned effect cannot be obtained. If the content of Constituent B is more than 20 wt. %, although the hardness of the aluminum alloy increases, the ductility, critical upsetting ratio, and other properties deteriorate, reducing the forgeability.
The elements Mg and Li, which are used in Constituent C, have an effect that they can increase the hardness of the aluminum alloy when they are rapidly solidified in xcex1-aluminum to form a supersaturated solid solution. If the content of Constituent C is less than 0.1 wt. %, the above-mentioned effect cannot be obtained. If the content of Constituent C is more than 20 wt. %, although the hardness of the aluminum alloy increases, the ductility, critical upsetting ratio, and other properties deteriorate, reducing the forgeability.
When Constituents D, B, and C are added with the specified contents as shown above, because the aluminum having Constituent C as a solid solution has fine crystal grains and because the intermetallic compounds are deposited or crystallized out at grain boundaries, a structure is formed that has less tendency to overgrow with temperature. The formation of this structure enables the production of an aluminum alloy with superior balance between the hardness and forgeability.
If any one of Constituents D, B, and C lies beyond the specified range of content, the balance between the hardness and forgeability is destroyed, producing high hardness with low forgeability or high forgeability with low hardness.
In the aluminum alloy of the second aspect of the present invention, it is more desirable that the content of Constituent C be more than 5 wt. % and not more than 20 wt. %.
This content range, when the surface of the aluminum alloy is anodized to form an anodic oxide coating, enables the anodic oxide coating to obtain a shade of relatively low brightness such as brown or dark gray. The shade of the anodic oxide coating can be changed by adjusting the kind and content of elements used in Constituent C and other Constituents.
In the aluminum alloys of the first and second aspects of the present invention, it is more desirable that the aluminum alloys be further provided with an anodic oxide coating.
As mentioned above, the shade of an anodic oxide coating can be changed by adjusting the kind and content of elements used in the individual Constituents. This enables the production of aluminum alloys provided with anodic oxide coatings having different shades. As a result, the painting process of the product can be omitted by using an anodic oxide coating having relatively high hardness as the protective coating of the aluminum alloy and by adjusting the shade of the anodic oxide coating so as to conform to the shade required in the product using the aluminum alloy. Consequently, the manufacturing cost of the product using the aluminum alloy can be reduced.
In the aluminum alloys of the first and second aspects of the present invention, it is more desirable that the anodic oxide coating have a lightness less than 50.
The lightness is measured by spectrophotometric colorimetry using a chromaticity meter (Japanese Industrial Standard JIS Z 8729: the L*a*b* color-expressing system). The light source for the measurement is D65 (the International Lighting Committee: the ISO standard light) with a color temperature of 6,504K.
In the aluminum alloys of the first and second aspects of the present invention, the anodic oxide coating may be formed on the surface of an aluminum-alloy base material. In this case, the base material may have an electrical conductivity less than 20% IACS (International Annealed Copper Standard).
The present inventors have found that as the electrical conductivity of a base material decreases, the base-material element forms more solid solutions with the anodic oxide coating, giving a shade of relatively low brightness such as brown to the anodic oxide coating. The present inventors have also found that the base material requires to have an electrical conductivity less than 20% IACS in order to give a shade of relatively low brightness such as brown to the anodic oxide coating.
In the aluminum alloys of the first and second aspects of the present invention, the anodic oxide coating may have a shade of brown, dark gray, or dark brown.
When a component is required to have a low-bright shade such as brown in the final product, the use of the aluminum alloy of the present invention makes it possible to obtain the required shade by adjusting the kind and content of elements used in the individual Constituents. This simplifies the traditionally required painting process of the component. Consequently, the manufacturing cost of the component can be reduced.
The aluminum alloys of the first and second aspects of the present invention may have aluminum crystals and intermetallic compounds. In this case, the aluminum crystals may have an average grain diameter of 1,000 nm or less and the intermetallic compounds may have an average grain diameter of 500 nm or less.
This enables the aluminum alloy to obtain high forgeability without losing the high hardness.
If the aluminum crystals have an average grain diameter more than 1,000 nm or the intermetallic compounds have an average grain diameter more than 500 nm, although the aluminum alloy improves its forgeability by improving its ductility, critical upsetting ratio, and other properties, it decreases its hardness.
In the aluminum alloys of the first and second aspects of the present invention, it is more desirable that the aluminum crystals have an average grain diameter of 500 nm or less and that the intermetallic compounds have an average grain diameter of 300 nm or less.
This enables the aluminum alloy to obtain higher hardness without losing its forgeability such as ductility and critical upsetting ratio when higher hardness is required.
The aluminum alloys of the first and second aspects of the present invention may have a Rockwell B hardness (HRB) not less than 50 and not more than 100. In this case, the aluminum alloy may have a critical upsetting ratio of 70% or more at temperatures not lower than 200xc2x0 C. and not higher than 600xc2x0 C. and an elongation of 10% or more at 20xc2x0 C.
The hardness HRB not less than 50 and not more than 100 means sufficiently high hardness in comparison with the conventional ingot aluminum alloys such as A5052. This high hardness suppresses the generation of surface flaws during the manufacturing process, thereby significantly reducing the ratio of defective products due to the surface flaws. If the hardness HRB is less than 50, as in the conventional ingot aluminum alloys, it, is difficult to suppress the generation of surface flaws during the manufacturing process. If the hardness HRB is more than 100, such properties as the elongation at 20xc2x0 C. and critical upsetting ratio deteriorate, reducing the forgeability.
The use of an aluminum alloy having the above-described critical upsetting ratio and elongation allows one or two processes of hot-working at temperatures not lower than 200xc2x0 C. and not higher than 600xc2x0 C., facilitating the near-net-shape forging of components with complicated shapes. If the aluminum alloy has a critical upsetting ratio less than 70% at temperatures not lower than 200xc2x0 C. and not higher than 600xc2x0 C. or an elongation less than 10% at room temperature (20xc2x0 C.), one or two processes of hot-working (near-net-shape forging) for obtaining components with complicated shapes generates work cracking of the components during the forging.
It is more desirable that the aluminum alloy of the first aspect of the present invention comprises (1) not less than 1.5 wt. % and not more than 2.5 wt. % Constituent A, (2) not less than 3 wt. % and not more than 6 wt. % Constituent B, (3) not less than 4 wt. % and not more than 6 wt. % Constituent C, and (4) not less than 1 wt. % and not more than 1.5 wt. % Constituent D.
The above-mentioned selection of the content ranges of Constituents A, B, C, and D enables the aluminum alloy to obtain a more enhanced balance between the hardness and workability (forgeability).
It is more desirable that the aluminum alloy of the second aspect of the present invention comprises (1) not less than 1.5 wt. % and not more than 2.5 wt. % Constituent D, (2) not less than 3 wt. % and not more than 6 wt. % Constituent B, and (3) not less than 4 wt. % and not more than 6 wt. % Constituent C.
The above-mentioned selection of the content ranges of Constituents D, B, and C enables the aluminum alloy to obtain a more enhanced balance between the hardness and workability (forgeability).
The third aspect of the present invention offers a method for manufacturing an aluminum-alloy member made of the following aluminum alloy: The aluminum alloy comprises (1) not less than 0.1 wt. % and not more than 8 wt. % Constituent A comprising one or more kinds of elements selected from the group consisting of titanium (Ti), vanadium (V), hafnium (Hf), and zirconium (Zr), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li). First, a preform comprising the aluminum alloy is produced. Next, the preform is heated up to a temperature not lower than 200xc2x0 C. and not higher than 600xc2x0 C. at a temperature rising rate of not less than 2xc2x0 C./sec and not more than 200xc2x0 C./sec. Then, the heated preform is subjected to hot-working.
This procedure enables the easy production of an aluminum-alloy member having high hardness and a complicated shape notwithstanding the considerably reduced number of times of working during the hot-working process in comparison with the conventional methods.
If the temperature during the heating process (degasification process) of the preform is higher than 600xc2x0 C. or the temperature-rising rate is less than 2xc2x0 C./sec or more than 200xc2x0 C./sec, the hot-working produces an aluminum alloy with sec or more than 200xc2x0 C./sec, the hot-working produces an aluminum alloy with reduced hardness resulting from the coarsened grains of aluminum crystals and intermetallic compounds. If the heating temperature of the preform is lower than 200xc2x0 C., it is difficult to give the preform sufficient strength because of the insufficient bonding between the grains constituting the preform. This reduces the critical upsetting ratio at temperatures not lower than 200xc2x0 C. and not higher than 600xc2x0 C. and an elongation at room temperature (20xc2x0 C.), deteriorating the forgeability.
In the method for manufacturing an aluminum-alloy member in the third aspect of the present invention, the aluminum alloy may further comprise not less than 0.1 wt. % and not more than 5 wt. % Constituent D comprising one or more kinds of elements selected from the group consisting of niobium (Nb), molybdenum (Mo), silver (Ag), iron (Fe), cobalt (Co), tantalum (Ta), and tungsten (W).
The fourth aspect of the present invention offers a method for manufacturing an aluminum-alloy member made of the following aluminum alloy: The aluminum alloy comprises (1) not less than 0.1 wt. % and not more than 5 wt. % Constituent D comprising one or more kinds of elements selected from the group consisting of niobium (Nb), molybdenum (Mo), silver (Ag), iron (Fe), cobalt (Co), tantalum (Ta), and tungsten (W), (2) not less than 0.1 wt. % and not more than 20 wt. % Constituent B comprising one or more kinds of elements selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), mischmetal (Mm), calcium (Ca), strontium (St), and barium (Ba), and (3) not less than 0.1 wt. % and not more than 20 wt. % Constituent C comprising one or more kinds of elements selected from the group consisting of magnesium (Mg) and lithium (Li). First, a preform comprising the aluminum alloy is produced. Next, the preform is heated up to a temperature not lower than 200xc2x0 C. and not higher than 600xc2x0 C. at a temperature rising rate of not less than 2xc2x0 C./sec and not more than 200xc2x0 C./sec. Then, the heated preform is subjected to hot-working.
This procedure enables the easy production of an aluminum-alloy member having high hardness and a complicated shape notwithstanding the considerably reduced number of times of working during the hot-working process in comparison with the conventional methods.
If the heating temperature of the preform is higher than 600xc2x0 C. or the temperature-rising rate is less than 2xc2x0 C./sec or more than 200xc2x0 C./sec, the hot working produces an aluminum alloy with reduced hardness resulting from the coarsened grains of aluminum crystals and intermetallic compounds. If the heating temperature of the preform is lower than 200xc2x0 C., the preform becomes brittle because of the insufficient bonding between the grains constituting the preform. This reduces the critical upsetting ratio at temperatures not lower than 200xc2x0 C. and not higher than 600xc2x0 C. and an elongation at room temperature (20xc2x0 C.), deteriorating the forgeability.
In the methods for manufacturing aluminum-alloy members in the third and fourth aspects of the present invention, it is more desirable that the heating temperature of the preform be not lower than 350xc2x0 C. and not higher than 450xc2x0 C.
The above-mentioned selection of the heating temperature enables the aluminum-alloy member to easily obtain a more enhanced balance between the hardness and forgeability.
In the methods for manufacturing aluminum-alloy members in the third and fourth aspects of the present invention, it is desirable that the die temperature for the hot-working be about 400xc2x0 C.
In the methods for manufacturing aluminum-alloy members in the third and fourth aspects of the present invention, the step for producing the preform may include a step for forming rapidly solidified powders of aluminum alloy.
In the methods for manufacturing aluminum-alloy members in the third and fourth aspects of the present invention, the step for producing the preform may employ the OSPREY method.
In the methods for manufacturing aluminum-alloy members in the third and fourth aspects of the present invention, the step for producing the preform may include a step for forming powders produced by pulverizing rapidly solidified ribbons of aluminum alloy.